The invention relates to a drive device for producing a sinusoidal speed pattern for a transport belt provided for transporting sheets or signatures in a printing machine.
Speed patterns or vignettes of this type are run, in particular, by transport belts which, in the feeder of a sheet-fed rotary printing machine, feed sheets individually or imbricated, i.e., overlapped, from a sheet pile to the printing machine. In this regard, before the direct transport from the feeding table to the printing machine, the sheet is aligned on so-called front lays or marks. In order that the leading edge of each individual sheet be protected when it engages the front lays, contact therebetween occurs at a low speed of the sinusoidal speed pattern of the transport belt.
For producing such a speed pattern, the Japanese Utility Model (JP-GM) Sho 61-83924 discloses the practice of driving the drive roller of an endless transport belt guided around a further deflection roller by eccentrically mounted gearwheels. In this regard, this Japanese utility model utilizes a gear train having three eccentrically mounted gearwheels. In practice, it is very complicated to align exactly with one another gear wheels which have teeth engaging eccentrically with one another.
It is accordingly an object of the invention to provide an alternative drive device for producing a sinusoidal speed pattern for a transport belt which avoids the disadvantages of the heretofore known drive devices of this general type.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a drive device for producing an at least approximately sinusoidal speed pattern for a transport belt provided in a printing machine for transporting printing material selected from the group thereof consisting of sheets and signatures, comprising non-round drive wheels rotatable about respective axes thereof, and a tensioning member by which the drive wheels are drivingly connected.
In accordance with another aspect of the invention, there is provided a drive device for producing an at least approximately sinusoidal speed pattern for a transport belt provided in a printing machine for transporting printing material selected from the group thereof consisting of sheets or signatures, comprising eccentrically mounted drive wheels having a circular contour and being rotatable about respective axes thereof, a non-round compensating wheel, and a common flexible tensioning member for drivingly connecting the drive wheels and the compensating wheel to one another.
In accordance with another feature of the invention, the compensating wheel is pivotably mounted.
In accordance with a further feature of the invention, the compensating wheel is displaceably mounted.
In accordance with an added feature of the invention, the drive wheels are toothed belt pulleys, and the flexible tensioning member is a toothed belt.
In accordance with a concomitant feature of the invention, the drive wheels are sprockets, and the flexible tensioning member is a chain.
A particular advantage of the invention is that the provided drive wheels do not mesh directly with one another but are drivingly connected only indirectly by a flexible tensioning member such as a toothed belt or chain. As a result of this feature, the quality requirements imposed upon the drive wheels are low, in relation to both the strength and accuracy thereof, because the flexible tensioning member, due to the elasticity thereof, compensates for inaccuracies which may possibly occur. Assembly is likewise quite simple.
In a second exemplary embodiment, provision is made for the drive wheel for the drive roller of the transport belt to be formed round and to be mounted eccentrically, and also to form the drive wheel driven with a single revolution by the printing machine likewise round and to mount it eccentrically. Furthermore, provision is made for a third non-round, ellipse-like deflection wheel, which keeps the common flexible tensioning member always uniformly in tension.
The deflection wheel is mounted so that it can be pivoted or displaced, and therewith also provided at the same time as a tensioning wheel for the flexible tensioning member.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an eccentric belt drive, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: